Vibrating screen



Ju'ne 2s,-19 23.

WITNESS;

F1 led] Oct. 1918 B. A. MITCHELL 'VIBRATING SCREEN 2 Sheets-Sheet 1 6; %%AT TORNEY$ Jae L 1 20 J [NVEN TOR.

June '26, 1923. 1,459,840

5. A. MITCHELL VIBRATING SCREEN Fil ed 001:. 2 1918 2 Sheets-Sheet 2 [NVEN TOR. M {flag {70% f iZZkeE Patented June 26, 1923.

UNITED STATES PATENT OFFICE.

BENJAMIN A. MITCHELL, F GARFIELD, UTAH, ASSIGNOR OI" TWO-THIRDS TO MINNIE L. MITCHELL, OF MAGNA, UTAH.

VIBRATING SCREEN.

Application filed October 21, 1918.

To all 20720722. it may concern:

Be it known that I, BENJAMIN A. MITCH- ELL, a citizen of the United States, residing at Garfield, in the countv of Salt Lake and State of Utah, have invented certain new and useful Improvements in Vibrating Screens, of which the following is a specification.

This invention relates to improvements in screening machines, and its principal purpose is to provide improved methods of and means for arranging and mounting the screening medium. The invention is of particular advantage in connection with vibrating screens of the inclined type, in which the crushed rock, coal, or other material to be screened, enters at the upper edge of the screen and is screened as it passes downwardly over the surface thereof under the action of gravity and the vibration of the screen. The principal object of the invention is to mount or arrange the screen cloth, or other screening medium, in such a manner that the progress of the material to be screened will be retarded as it passes downward along the screen surface. A further object is to provide a screen of the inclined type in which the progress of the material to be screened is retarded by changing the slope of the surface, thereby allowing the fine particles of said materials more time in which to find passage through the meshes of the screen as the material approaches the lower edge thereof, where the fine particles have become fewer in number. Where the screen cloth has a constant slope throughout its length these fine particles have a lesser tendency to pass through the screen adjacent the lower edge thereof than in the screens of the present invention, in which the progress of the materials is gradually retarded as they approach the lower edge. The present invention, therefore, produces a more thorough separation of the finer particles from the coarser particles, and a more even distribution of the screening function throughout the surface of the screen. Still another object of the invention is to make the upper half of the screen cloth, in which the greater wear always occurs, replaceable, without the necessity of replacing the lower half of the screen, in which the wear is much less. This replacement is made possible by constructing the screen of a plurality of complementary sections. Other objects of Serial No. 258,981.

the invention relate to various features of construction and arrangement, which will be set out more fully hereinafter.

The nature of the invention will be understood from the following specification, taken in connection with the accompanying drawlngs, invention are illustrated.

In the drawings- Figure 1 shows a top plan view of a vibrating screen embodying one form of my invention;

Fig. 2 is a sectional view, taken on the line 2-2 of Fig. 1, looking in the direction of the arrows;

Fig. 3 shows a sectional view, similar to Fig. 1, illustrating the application of the invention to another form of screening apparatus, commonly known as the whip-tap screen;

Fig. 4 shows another sectional view, similar to Fig. 2, illustrating the application of the invention to still another form of screen ing apparatus.

Fig. 5 illustrates another modification of the invention, in which a vibrator of the form illustrated in Figs. 1 and 2 is mounted below a screening medium comprising three separate sections.

Fig. 6 is a view similar to- Fig. 2, showing similar vibrating mechanism applied to a screen having a curved cross section in a vertical plane; and

Fig. 7 shows a. sectional view, similar to Fig. 2, illustrating a curved screen made in two sections with the vibrating apparatus mounted below the screen, as in Fig. 5.

The form of the invention illustrated in Figs. 1 and 2 comprises a supporting structure 10, having an inclined wall 10 a rear wall 10 a front wall 10, and end walls 10 forming an enclosure divided by a partition 11 to form a bin or receptacle 12 for the fine materials and another receptacle 13 for the coarse materials separated by the action of the screening medium. A rectangular screen frame 15 is mounted in an inclined position above the inclined wall 10, and supported at its upper ed e by hinges, 16, which are mounted on the upper wall 10 of the supporting structure. Projecting plates 17 are attached to the lower edge of the screen frame 16, and these plates are connected, throu h rods 18 and turn-buckles 19, with other plates 20 which are secured to the end in which several embodiments of the walls 10 of the supporting structure, so that by adjusting the turn-buckles the inclination of the screen frame and the screening medium may be changed as desired. The screening medium 21, mounted within the screen frame, comprises two sections 21 and 21 formed of metallic screen cloth, or other suitable material, of any desired mesh and stiffness, these sections being relatively long and narrow, and arranged to meet along the middle portion of the screen. The opposite ends of the sections 21" and 21 are connected to tubular slotted gripping members 22, of the form particularly described in my copending applications Ser. No. 209,920, filed January 2, 1918, and Serial No. 232,798,

filed May 6, 1918. These gripping members are provided with apertured lugs 23, en gaged by the angular extremities of the adjusting screws 24 which extend through suitable apertures in the end frame members of the screen frame and are threadedly en gaged on the projecting ends thereof by means of the hand wheels 25. In the embodiment shown two adjusting screws and hand wheels are provided at each end of each section of the screen, and by manipulation of these hand wheels it is possible to secure and maintain any desired degree of tension in the screen medium. In most cases, and particularly when the screening medium is lacking in stiffness, it is desirable to stretch the screen and maintain it under an extremely high tension. It will be observed that the arrangement of the adjusting screws in the supporting frame is such that the upper section 21 of the screening medium is inclined downwardly at a greater pitch than the lower section 21 so that material fed onto the screen is gradually retarded as it approaches the lower edge of the screen.

The finer crushed ore, or other material to be screened is fed thereto from a container 26, through a chute 27 from which it passes onto the surface of a roll feeder 28, which is rotated in the direction indicated by the arrow through suitable driving mechanism. The material is carried around by this roll feeder and distributed onto the inclined plate 29 which forms the lower wall of a hopper 30. The material thus distributed throughout the length of the hopper passes through the slotted opening in the lower part thereof onto the upper edge of the screen 21.

The screen 21 is vibrated, in the embodiment of the invention illustrated in Figs. 1 and 2, by means of a vibrator of the form particularly described in my copending applications above referred to. This vibrator comprises a casing 32, having an electric motor or other driving means mounted in the central portion 33 thereof. The shaft of the motor is directed into each of the end casings 34, having mounted therein an unbalanced rotary vibrator, so that high frequency vibrations are set up in the end casing. The central portion 33 of the casing is mounted upon a supporting member 35, which is secured to and extends upwardly from the lower frame member of the screen frame 15. The end casings 34 of the vibrator are preferably tapered outwardly, and are adapted to be closely fitted by the rings 36, which are secured thereon by transverse keys 37. The rings are riveted, or otherwise secured, to the transmitting plates 38, which extend downwardly, and which preferably have wooden strips 39 secured to the lower edges thereof. The lower edges of the plates 38 are constructed to conform to the contour of the screen, so that the upper portion of each plate rests upon and coacts with the portion 21 of the screening medium, while the lower portion of the plate rests upon and coacts with the portion 21 of the screening medium. As the vibrator is driven at a high speed by the electric motor mounted therein, the end casings 34 are caused to vibrate at a high frequency, so that each and every point of the end casing describes a series of minute circular movements of small diameter. This vibratory movement is imparted through the plates 38 to the screen cloth, and as the finely divided material passes downwardly thereover, it is effectively screened. As the material passes over the upper portion of the screen cloth, where the proportion of relatively fine particles is comparatitvely large, a large portion of these particles will pass through the screen, which in this location has a relatively steep slope. hen the materials pass by gravity onto the lower portion of the screening medium, the material is retarded, thus giving the finer particles, which are now relatively few in number, a sufficient opportunity to pass through the screening medium before the lower edge thereof is reached. In this way the screening action is distributed over the entire screening surface, and a more perfect result is obtained.

In Fig. 3 of the drawings I have illustrated the application of my invention. to another form of screening machine, in which a series of impulses are imparted to the screen-- ing medium by rotating cams. In the form of construction illustrated a rectangular screen frame 40 is mounted in position above the bin 41, adapted to receive the fine screened materials, and another bin 42 is provided adjacent the lower edge of the screen frame to receive the coarse materials.

The material to be screened may be fed to i screen. The screen 48 in'this embodimentis formed in two sections 48 and 48 which are connected to the end frame members of the screen frame in the manner illustrated in Figs. 1 and 2, the tension of the screen being adjusted by the hand wheels 49. The upper section48 has a relatively steep slope, while the lower section 48 has a lesser slope, designed to retard the progress of the materials thereover, although the screen as awhole is mounted in an inclined position. Impulses are imparted to the screening medium through posts 50, which are attached to the screen cloth by plates 51. The upper ends of the posts are adapted to be engaged by hammers 52, which are'carried'by spring plates 53, secured at 54: to a member 55 car ried by the screen frame. The ends of the spring members 53, opposite the points 54, are adapted to be engaged by the teeth 56 of cams 56, which are secured to shafts 57 and 58. These shafts are connected by suitable pulleys 59 and a cross belt 60, and one of the shafts is driven through a belt 61 from a suitable source of power, so that as the cams rotate in the direction indicated by the arrows the ends of the'spring plates 53 are intermittently lifted up and then allowed to fall again, causing the hammers 52 to strike the post 50. In this way a serles of impulses is imparted to the screening medium.

In Fig. 4 I have illustrated the application of the invention to another form of screening machine, comprising a screen frame 65, of rectangular form. mounted in an inclined position and adapted to have the finer ground material fed thereto in any desired manner, as, for example, by means of a feeding mechanism similar to that illustrated in Figs. 2'an d 3 and comprising a hopper 66. The screen 67 is formed in two sections 67 and 67 the upper section 67 having a greater slope than the lowe section 67". These screen sections are mounted in the screen frame in the .manner illustrated in Figs. 1 and 2, the tension of the screen being adjusted by the hand wheels 68. The screen is vibrated through members 69, which are attached to the central portions of the screen sections by plates 7 O, and which are rigidly secured at their lower ends to the resilient members 71. These members are rigidly secured at their outer ends to the screen frame 65, as shown at 72, and their inner ends are adapted to be tripped intermittently by rollers 73 on a revolving wheel or cam 74:, which rotates in the direction indicated by the arrow. As these members are tripped they vibrate in the manner of a tuning fork, and thus impart impulses to the screen cloth.

In Fig. .5 of the drawings there is illustrated a modification of the form of con struction illustrated in Figs. 1 and 2. In

manner heretofore described, so that the tension of each section may be independently adjusted through the hand wheels 78. The middle section 77 overlaps the upper edge of the lower section 77, and the upper section 77 in turn overlaps the middle section. The middle section has a lesser slope than the upper section, and the lower section has a lower slope than the middle section, so that the cross section of the screen approximates a curve and serves to retard the progress of the materials passing clownwardly thereover. In this form of the invention a vibrator 79, of the form illustrated in Figs. 1 and 2, is mounted below the screen cloth and supported on a member 80. Rings 81 are attached to the ends of the vibrator casing, and these are connected through transmitting plates 82 to the vari ous sections of the screen cloth which rest upon the upper edges thereof. This construction has the advantage that the weight of the material on the screen serves to maintain a tight contact between the upper edges of the transmitting members 82 and the screening medium.

In Fig. 6 I have shown still another embodiment of the invention, in which a rectangular frame 85 is mounted in inclined position and adapted to support a screen to which material is fed through a hopper 86. The screening medium 87 is formed in one piece, but is curved downwardly, as illustrated, so that the slope of the screen gradually decreases as the lower edge thereof is approached. The tension of the screen is adjusted by the hand wheel 88, and vibra tions are imparted thereto by a rotary vibrator 89, of the form previously described, having plates 90 connected thereto for transmitting the vibrations to the screen. The lower edges of these plates are provided with members 91 of wood, or the like, which conform to the contour of the screen and contact therewith. As in the previously described form'of the invention the vibrator is supported by a member 92 extending upwardly from the lower edge of the screen frame.

In Fig. 7 I have illustrated a modification of the construction illustrated in Figs. 5 and 6. In this construction the screen medium 94 is formed in two sections 94 and 949, each of which is curved in cross section and mounted in the screen frame 95,- in such amanner as to permit the adjustment of the tension thereof by the hand wheels 96. The rotary vibrator 97 is mounted below the screen as in the embodiment illustrated in Fig. 5, and is connected to the screen through plates 98, the upper edges of which form the contour of the screen sections. The material to be screened is fed to the screening medium through suitable feeding devices comprising a hopper 99. 1

Although I have shown and described various forms of screening machines for the purpose of illustrating the nature and application of my invention, it will be under stood that it may be constructed in various different forms without departing from the scope of the appended claims.

"What I claim is:

1. The combination in a screening machine, of a stationarily supported screening medium, means for mounting said screening medium iin an inclined position with the lower parts thereof having a lesser slope than the upper parts thereof, means for introducing loose materials on to the upper part ofsaid screening medium, and means for producing aibstantially circular vibrations in said screening medium as said ma terials pass thereover.

2. The combinationin a screening machine, of a stationary screening medium, means for mounting said scres-zning medium in an inclined position with the lower parts thereof having a lesser slope than the upper parts thereof, means for introducing loose materials on to the upper part of said screening medium, and means for imparting high frequency vibrations directly to said screen.

3. The combination in a screening machine, of a screening medium mounted in an inclined position, said screening medium being divided longitudinally into a plurality of complementary sections, means for causing loose materials to pass downwardly by gravity over said screening medium, means for producing tension in said sections of said screening medium transversely to the path of travel of said materials thereover, and means for producing circular vibrations in said screening medium.

4. The combination in a screening machine, of a stationary screen frame mounted inan inclined position, a screening medium divided longitudinally into a plurality of sections, means for connecting the ends of said sections to said frame, means for in troducing finely divided materials on to the upper part of said screening medium, and means for producing circular vibrations in said screening medium.

5. The combination in a screening machine, of a stationary screen frame mounted in an inclined position, a screening medium divided longitudinally into a plurality of sections, means for connecting the ends of said sectionsto said frame and for producing tension in said sections longitudinally thereof, means for introducing finely divided materials on to the upper part of said screening medium, a vibrator having its casing mounted in fixed position with respect to said frame and having a. vibratory part, and means connected to said vibratory part for transmitting vibrations to said screening medium in a plane perpendicular to the direction in which tension is applied tosaid screening medium. 1

6. The combination in a screening machine, of a stationary screen frame mounted in an inclined position, a screening medium divided longitudinally into a plurality of sections, means for connecting the ends of said sections to said frame and for producing tension in said sections longitudinally thereof, means for introducing finely divided materials on to the upper part of said screening medium, a vibrator located beneath said screening medium, means for supporting said vibrator in a relatively fixed position with respect to said frame, and means connected to said vibrator and extending upwardly therefrom to transmit vibrations to said screening medium in a plane perpendicular thereto.

7. The combination in a screening machine, of a stationary screen frame mounted in an inclined position, a screening medium divided longitudinally into a plurality of sections, means for connecting the ends of said sections to said frame and for producing tension in said sections longitudinally thereof, means for introducing finely divided materials on to the upper part ofsaid screening medium, a vibrator located beneath said screening medium, means for supporting said vibrator in a relatively fixed position with respect to said frame, and a plate carried by said vibrator and extending upwardly therefrom with its upper edges coacting with the under sides of said sections of said screening medium.

8. The combination in a screening machine, of a rectangular screen frame mounted in an inclined position, a screening medium divided longitudinallyinto a plurality of complementary sections, means for independently securing the ends of said sections to the ends of said frame and producing tension in said sections, means for introducing loose materials on to the upper part of the upper section, the inclination of said sections to the horizontal decreasing toward the lower part of said frame, a vibrator easing mounted beneath said screening medium in a relatively fixed position with respect to said frame, means for producing substantially circular vibrations in the free ends of said casing, and plates carried by the free ends of said casing and extending upwardly to coact with the said sections of said screen,

the upper edges of said plate being shaped to conform to the contour of the composite screening medium.

9. In a screening machine, thecombination with a stationarily supported screen comprising a plurality of sections disposed at varying inclinations, of a vibrator arranged to execute harmonic motion in a plane transverse to the planes of said sec tions, and means for imparting said motion with substantially uniform amplitude simultaneously to each of said sections.

10. In a screening machine, the combination with a stationarily supported screen comprising a plurality of sections disposed at varying inclinations, said sections being arranged to have the material to be screened pass successively from those of the greater.

tude simultaneously to each of said sections.

11. In a screening machine, the combination with a stationarily supported screen comprising a plurality of sections disposed at varying inclinations, of independent tension adjusting devices for each of said sections, a vibrator arranged to execute harmonic motion in a plane transverse to the planes of said sections, and means for imparting said motion with substantially uni form amplitude simultaneously to each of said sections.

12. In a screening machine, the combination with a stationarily supported screen frame, of a plurality of screen sections in said frame arranged at varying inclinations, independent devices for adjusting individually the tension of each section, and means for feeding material to be screened upon the uppermost screen section.

In testimony whereof, I have subscribed my name.

BENJAMIN A. MITCHELL. 

